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Project Name: Evaluation of Alternatives for Dyebath Reuse
Country: None Listed
Description: In many cases, salts from textile dyeing and finishing operations are a significant factor in causing aquatic toxicity. Salts used in dyeing, alkalis and acids enter the wastestream and are not removed using conventional wastewater treatment technology. Salt removal requires advanced wastewater treatment technologies such as ion exchange and is very difficult and costly. Consequently, the reduction of salt in the effluent is most efficiently addressed by reducing the amount of salts and acids used and reusing salt. Use of low salt dyes and improved process control to minimize chemical usage are essential for reducing the amount of salt discharged. However, recovery and reuse of salts may be required to comply with aquatic toxicity standards. The feasibility of dyebath reuse for salt recovery was examined using ozonation and membrane filtration treatment alternatives. Individual studies were performed for each treatment technology. Dyebaths from designated dye machines were segregated and treated. Ozonation provided color removal and oxidation of some organics. Since the salt concentration was not altered, filtration and recycle of the decolorized, ozonated dyebath allowed reuse of the salts. Ultrafiltration followed by nanofiltration concentrated dyes and other large molecular weight organics producing a permeate clear in color and containing most of the salts. Essentially all of the chlorides passed through the membrane, however, approximately 20% of the sulfates were rejected and were retained in the concentrate. Reuse of the ozonated dyebath was successful for dyeing of fabrics with dark shades. However, dyeing of light shade fabrics was not acceptable. Dyeing of fabrics using membrane permeate was acceptable for all shades. It was determined that approximately 30% to 40% of the salts could be recovered using either ozonation or membrane treatment. Capital and operating costs were determined for each technology and found to be similar. Membrane treatment provided a more consistent and higher quality effluent than ozonation. The reuse of membrane treated dyebath also provided higher quality dyeing.
 

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